10 THE PEOTOZOA 



a. The cuticle forms a protective covering for the 



whole surface. It is thickest on the stalk, and 

 the straightening out of the stalk after contraction 

 probably depends upon its elasticity. 



b. Cilia are restricted to the peristome, the margin of 



the disc, the vestibule, and the pharynx. They 

 produce a current which runs round the disc in 

 the direction opposite to that of the hands of a 

 watch, then down the vestibule near its ventral 

 surface, and, after a turn in the upper part of the 

 pharynx, up along the dorsal wall of the vestibule 

 to the exterior. The appearance of a long vibra- 

 tile ' vestibular seta ' in the dorsal part of the 

 vestibule is probably due to the movements of the 

 vestibular cilia. 



c. A longitudinal ' myophan ' striation is visible in the 



deeper layer of the ectosarc, especially in the 

 lower part of the body close to the stalk. 



d. The contractile band running down inside the 



cuticular sheath of the stalk is continuous above 

 with the deeper, ' myophan,' layer of the ecto- 

 sarc of the body. The spiral shortening of the 

 stalk is due to its contraction. In a specimen in 

 which this band had been broken, it was seen to 

 be drawn up suddenly towards the body at each 

 inversion of the disc, the stalk, however, remaining 

 straight. 



2. The endosarc is the more fluid granular central portion 

 of the cell-protoplasm. It does not extend into the 

 stalk. 



a. The food vacuoles circulate with the endosarc. 



b. The nucleus is an elongated curved band in the 



upper part of the body near the pharynx. 



c. The single pulsating vacuole is spherical and situated 



between the disc and the vestibule. 



